ISOLATION AND CHARACTERIZATION OF A NOVEL PERCHLORIC ACID-SOLUBLE PROTEIN INHIBITING CELL-FREE PROTEIN-SYNTHESIS

We found a novel protein in the postmitochondria supernatant fraction of rat liver, which is soluble in 5% perchloric acid and strongly inhi bits protein synthesis in a rabbit reticulocyte lysate system, The pro tein extracted from the supernatant fraction with 5% perchloric acid w as purified by ammonium sulfate fractionation and CM-Sephadex chromato graphy, The protein was shown to consist of two identical subunits wit h a molecular mass of 14 kDa. By immunoscreening with the rabbit antis era against the protein, a cDNA encoding the protein was cloned and se quenced. The cDNA contained an open reading frame of 411 base pairs en coding a 136-amino acid protein with a molecular mass of 14,149 Da. Th e deduced amino acid sequence was completely identical with that const ructed from all of the above peptides, Interestingly, the perchloric a cid-soluble protein inhibited cell-free protein synthesis in the rabbi t reticulocyte lysate system in a different manner from RNase A. The p rotein is likely to inhibit an initiation stage of cell-free protein s ynthesis, Among the rat tissues tested, the protein was located only i n liver and kidney, These findings are the first report on a new inhib itor that may be involved in the regulation of protein synthesis in th ose tissues.